Book/Report

FZJ-2018-04440

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Errors of absolute methods of reactor neutron activation analysis caused by non-1/E epithermal neutron spectra: the influence of the errors of the activities of the flux monitors when using the Bare Triple Monitor Method with Zr-094, Zr-096 and Au-197

Erdtmann, G. (Corresponding author)FZJ*

1993
Forschungszentrum Jülich GmbH Zentralbibliothek Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/19449

Report No.: Juel-2808

Abstract: A sufficiently accurate characterization of the neutron flux and spectrum, i. e. the determination of the thermal flux $\Theta_{th}$, the flux ratio, R$_{\Theta}$, and the epithermal flux spectrum shape factor, $\alpha$, is a prerequisite for all types of absolute and monostandard methods of reactor neutron activation analysis. A convenient method for these measurements is the bare triple monitor method with $^{94}$Zr, $^{96}$Zr and $^{197}$Au as flux monitors. However, the results of this method, especially with respect to $\alpha$ and $R_{\Theta}$, are very imprecise, because there are high error propagation factors form the counting errors of the monitor activities. On the other hand, error propagation factors from those of $\alpha$ and R$\Theta$ to the analytical resuits, i. e. the amounts of elements to be determined, is much smaller than one and, therefore, the contribution of the flux measurement to the total errors of the analytical resuits is mainly determined by the error of the flux monitor which preponderantly represents the thermal flux, i. e. by the counting error of $^{95}$Zr. This situation is comparable to that with relative methods, where errors of the activities of the standards (comparator samples) have a similar influence on the errors of the resuits. There are some exceptions from this general rule: These are nuclides with high cross-section ratios. In these cases the epithermal neutrons contribute considerable amounts to the ($\eta, \gamma$)-reaction rates. One would expect that with irradiation facilities with high flux ratios, i. e. where the thermal neutrons are strongly preponderant, also for these elements the errors would become very small. Unfortunately, from the investigations made up to now, there is no evidence for this effect. The reason for this finding is, that most irradiation facilities with high flux ratlos have also high $\alpha$-values, and they have an unfavourable influence on the error propagation factors. In the present report procedures are described to calculate the errors of the flux parameters, the $\alpha$-dependent cross-section ratios, and of the analytical results from the errors of the activities of the monitor isotopes. They are included in FORTRAN programs which also allow a graphical representation of the results. A great number of examples were calculated for ten different irradiation facilities in four reactors and for 28 elements. Plots of the results are presented and discussed.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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